Temperature gradient driven motion of magnetic domains in a magnetic metal multilayer by entropic forces

We studied the displacement of magnetic domains under temperature gradients in perpendicularly magnetized <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mi>Ta</a:mi> <a:mo>/</a:mo> <a:mo>[</a:mo> <a:mi>Pt</a:mi> <a:mo>/</a:mo> <a:msub> <a:mi>Co</a:mi> <a:mn>68</a:mn> </a:msub> <a:msub> <a:mi mathvariant="normal">B</a:mi> <a:mn>32</a:mn> </a:msub> <a:mo>/</a:mo> <a:msub> <a:mrow> <a:mi>Ir</a:mi> <a:mo>]</a:mo> </a:mrow> <a:mrow> <a:mo>×</a:mo> <a:mn>10</a:mn> </a:mrow> </a:msub> <a:mo>/</a:mo> <a:mi>Pt</a:mi> </a:mrow> </a:math> multilayer tracks with microfabricated Pt heaters and thermometers by magnetic force microscopy. Subtracting out the effects of the Oersted field from the heating current reveals the pure temperature gradient driven motion, which is always toward the heater. The higher the thermal gradient along the track is (owing to the proximity to the heater or larger heater currents), the greater the observed displacements of the domains are, up to a velocity of around 1 nm/s in a temperature gradient of 20 <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mrow> <c:mi mathvariant="normal">K</c:mi> <c:mo>/</c:mo> <c:mi>µ</c:mi> <c:mi mathvariant="normal">m</c:mi> </c:mrow> </c:math> . This velocity lies in the creep regime. Quantitative estimates of the strength of different driving mechanisms for the effect that have been proposed theoretically show that entropic forces dominate over those arising from the spin Seebeck and spin-dependent Seebeck effects in driving the domain motion.